Physical Vapor Deposition Target Constructions

ABSTRACT

The invention encompasses a method of bonding a first mass to a second mass. A first mass of first material and a second mass of second material are provided and joined in physical contact with one another. The first and second masses are then diffusion bonded to one another simultaneously with the development of grains of the second material in the second mass. The diffusion bonding comprises solid state diffusion between the first mass and the second mass. A predominate portion of the developed grains in the second material have a maximum dimension of less than 100 microns. The invention also encompasses methods of forming a physical vapor deposition target bonded to a backing plate.

TECHNICAL FIELD

[0001] The invention pertains to methods of bonding first and secondmasses to one another, and in particular embodiments, pertains tomethods of bonding two similar materials together, as well as to methodsof bonding physical vapor deposition target materials to backing platematerials.

BACKGROUND OF THE INVENTION

[0002] There are numerous applications in which it is desired to bond afirst mass to a second mass. One such application is in the bonding ofphysical vapor deposition targets (such as, for example, sputteringtargets) to backing plates. The backing plates are configured to retainthe targets in particular locations and orientations within pressurevapor deposition apparatuses.

[0003] Modern developments in physical vapor deposition methodologieshave created increasingly stringent requirements for robust bondingbetween targets and backing plates. A diagrammatic view of a portion ofan exemplary sputter deposition apparatus 10 is shown in FIG. 1.Apparatus 10 comprises a backing plate 12 having a sputtering target 14bonded thereto. A semiconductive material wafer 16 is within apparatus10 and provided to be spaced from target 14. Sputtered material 18 isdisplaced from target 14 and utilized to form a coating (not shown) overwafer 16.

[0004] Among the modern improvements in sputter design is an increase inthe distance between target 14 and semiconductive material substrate 16.Such increase in distance can enable more directional sputtering to beachieved over features of substrate 16 than can be achieved when target14 is close to substrate 16 by allowing atoms that are not movingperpendicular to substrate 16 to land on the sidewall of the sputteringchamber. Specifically, substrate 16 will frequently have vertical holesor slots (known as vias) with depths five times their width or more(i.e., having relatively high critical dimensions). It is difficult tosputter materials into vias having high critical dimensions unless thereis a relatively long throw between a sputtering target and a substratecomprising the vias.

[0005] Although the longer throw creates advantages in coverage relativeto shorter throw techniques, it also creates complications. One of suchcomplications is caused by additional power utilized in long-throwtechnologies. The additional power can cause sputtering targets to gethotter than they had in older methods. Such heat can disrupt a bondformed between backing plate 12 and target 14. For instance, if target14 is solder-bonded to backing plate 12, the heat developed duringlong-throw sputtering techniques can be sufficient to melt the solderbond and actually break target 14 free from backing plate 12.Accordingly, solder-bonding can be inappropriate for long-throwsputtering techniques.

[0006] A type of bonding which is generally able to withstand the hightemperatures utilized in long-throw sputtering techniques is diffusionbonding, which is a bond formed by solid state diffusion of componentsfrom target 14 to backing plate 12 and/or vice versa. A difficulty inusing diffusion bonding is that such typically comprises relatively hightemperatures (300° C. or more) to form the bond, and such temperaturescan adversely affect target materials. Accordingly, it can be difficultto develop diffusion bonding processes for bonding physical vapordeposition targets to backing plates, and which further retain desirableproperties of the physical vapor deposition targets. It would bedesirable to develop such diffusion bonding processes.

SUMMARY OF THE INVENTION

[0007] In one aspect, the invention encompasses a method of bonding afirst mass to a second mass. A first mass of first material and a secondmass of second material are provided and joined in physical contact withone another. The first and second masses are then diffusion bonded toone another simultaneously with the development of grains of the secondmaterial in the second mass. The diffusion bonding comprises solid statediffusion between the first mass and the second mass. A predominateportion of the developed grains in the second material have a maximumdimension of less than 100 microns.

[0008] In another aspect, the invention encompasses a method of forminga physical vapor deposition target bonded to a backing plate. A targetmaterial and a backing plate material are joined in physical contactwith one another. The target material and backing plate material bothcomprise aluminum. The joined target and backing plate materials arethermally treated under an atmosphere which is inert relative to formingoxides on the target and backing plate materials. The thermal treatmentsimultaneously diffusion bonds the target material to the backing platematerial while recrystallizing grains in the target material. Thediffusion bonding comprises solid state diffusion between the backingplate material and the target material to adhere the target material tothe backing plate material with a bond strength of at least 5,000pounds/inch². A predominate portion of the grains developed in thetarget material are less than 100 microns in maximum dimension after thethermal treatment of the target and backing plate materials.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

[0010]FIG. 1 is a diagrammatic view of a portion of a prior art sputterdeposition apparatus.

[0011]FIG. 2 is a flow chart diagram of a method encompassed by thepresent invention.

[0012]FIG. 3 is a diagrammatic illustration of a method of introducingwork hardening into a target material.

[0013]FIG. 4 is a diagrammatic illustration of the target material ofFIG. 3 with a backing plate at a preliminary bonding step.

[0014]FIG. 5 is a diagrammatic view of the target material and backingplate of FIG. 4 at a bonding step subsequent to that of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] This disclosure of the invention is submitted in furtherance ofthe constitutional purposes of the U.S. Patent Laws “to promote theprogress of science and useful arts” (Article 1, Section 8).

[0016] The invention encompasses methods of bonding materials to oneanother, and in particular embodiments encompasses methods of bonding aphysical vapor deposition target material to a backing plate material.

[0017] One aspect of the invention is a recognition that it would beadvantageous to develop methodologies for diffusion bonding analuminum-containing target to an aluminum-containing backing plate,while achieving relatively small grain sizes in the target material. Adifficulty associated with diffusion bonding of aluminum-containingtargets to aluminum-containing backing plates is that thediffusion-bonding temperatures can cause growth of crystalline grains(actually polycrystalline grains) in the aluminum targets. It isgenerally desired that aluminum grains remain relatively small (i.e.,less than 100 microns, and more preferably less than 50 microns) intargets comprising high purity aluminum (e.g., elemental aluminum), andaluminum alloys. The smaller grains can improve sputtering processes inwhich aluminum is sputtered from the target material relative tosputtering occurring from a target material having larger grains.

[0018] The invention encompasses methodology for controlling graingrowth associated with the diffusion bonding of aluminum. Suchmethodology can form a diffusion bonded aluminum sputtering target inwhich a predominate portion of the grains in the target material have amaximum grain size of less than 100 microns.

[0019] A method encompassed by the present invention is described by aflow diagram in FIG. 2. At an initial step (labeled 30 in FIG. 2) workhardening is done to the a target material. If, for example, the targetmaterial comprises aluminum, work hardening can be introduced bycompressing the aluminum from an initial thickness to a secondthickness. Such compression is illustrated in FIG. 3, wherein a target50 is illustrated before and after compression, with an arrow 52provided to indicate the step of compression. Target 50 comprises afirst thickness “X” prior to the compression 52 and a second thickness“Y” after the compression. The compression can be accomplished by, forexample, cold forging or cold rolling The final thickness of target 50(“Y”) can be, for example, less than 2% of the initial thickness oftarget 50 (i.e., a 98% compression), and is typically less than or equalto about 40% of the initial thickness of target 50 (i.e., a 60%compression). In particular embodiments, target 50 can be subjected to a95% compression (i.e., compressed so that final thickness “Y” is about5% of initial thickness “X”).

[0020] Target 50 can, for example, comprise or consist essentially oflow to high purity aluminum. An exemplary commercial (low-purity)aluminum that can be utilized for target 50 is 1100 series aluminumalloy. The material of target 50 can be cast as a billet having adiameter of from about 4 inches to about 9 inches, and having an initialthickness of from about 5 inches to about 10 inches. After thecompression of target 50, the resulting cold-worked blank can be cut toform a round blank of a desired diameter.

[0021] Referring again to the flow chart of FIG. 2, the target is joinedto a backing plate (FIG. 2, step 32). Preferably, the target and backingplate are cleaned prior to joining them to remove contaminants that maybe present. A method of joining a target to a backing plate is describedwith reference to FIGS. 4 and 5. Referring to FIG. 4, the work-hardenedtarget 50 of FIG. 3 is shown elevated above a backing plate 60. Backingplate 60 of FIG. 3 is shown having a continuous channel 62 machined intoa surface in a spiral pattern. Ultimately, target 50 will be pressedagainst plate 60 to force material from target 50 into channel 62.

[0022] In embodiments in which target 50 comprises high-purity aluminum,backing plate 60 can also comprise aluminum, and can specificallycomprise, for example, 2000 Series, 5000 Series, 6000 Series or 7000Series heat-treatable aluminum alloys. In particular embodiments,backing plate 60 can comprise heat-treatable aluminum alloy 6061 ineither a T4 or T6 precipitate hardened condition.

[0023] An initial step in bonding target 50 to backing plate 60 istypically to join the target and backing plate by physically contacttarget 50 with plate 60. Arrows 54 of FIG. 4 indicate such joining byshowing that target 50 is lowered onto plate 60. FIG. 5 shows anassembly 70 comprising target 50 joined to plate 60. In the shownassembly 70, target 50 covers channel 62 (FIG. 4) of backing plate 60.Although the shown embodiment has a channel formed in backing plate 60to enhance coupling of target 50 to backing plate 60, it is to beunderstood that such channel can be eliminated in particular embodimentsof the invention, or can be provided in target 50, rather than inbacking plate 60. In embodiments in which one of backing plate 60 andtarget 50 is harder than another of backing plate 60 and target 50,channel 62 will preferably be provided in the harder of the two, so thatthe softer of the two can be pressed into the channel in subsequentprocessing.

[0024] Assembly 70 is can be formed in, or placed in, an atmospherewhich is inert relative to oxide formation from materials of plate 60and target 50. In embodiments in which plate 60 and target 50 comprisehigh-purity aluminum, or aluminum alloys, the inert atmosphere cancomprise a vacuum, or consist essentially of, for example, one or moreof nitrogen gas and argon gas. The inert atmosphere preferably does notcomprise oxidative components (like oxygen), as such could adverselycause oxidation of the materials of one or both of the blank 60 andtarget 50.

[0025] Referring again to the flow chart of FIG. 2, the joined backingplate and target are thermally treated (step 34 of FIG. 2) tosimultaneously 1) diffusion bond the target to the backing plate, and 2)develop grains in the target. If target 50 and backing plate 60 comprisehigh-purity aluminum, the thermal treatment can comprise, for example,is heating the joined target and backing plate to a temperature ofbetween 280° C. and 400° C. (preferably between 300° C. and 340° C.),and maintaining such temperature for a time of from about 15 minutes toabout an hour. During the time that the temperature is maintained,target 50 and backing plate 60 can be compressed in a forge to pressureof from about 10,000 pounds per square inch (psi) to about 16,000 psi.

[0026] An exemplary thermal treatment procedure for treating a targetand backing plate which comprise aluminum is as follows. Initially, anassembly comprising a target joined against a backing plate is heated toa temperature of from about 280° C. to about 400° C. (preferably formabout 300° C. to about 350° C., and more preferably from about 300° C.to about 344° C.) and maintained at such temperature for a time of from15 to 30 minutes. The assembly is then transferred to a forge which isalso maintained at a temperature of from about 280° C. to about 400° C.The forge is utilized to compress target 50 and backing plate 60together to a temperature of from about 10,000 psi to about 16,000 psi.After compressing the target and backing plate, the assembly istransferred back to the furnace having a temperature of from about 280°C. to about 400° C., and maintained at such temperature for anadditional time of from about 10 minutes to about 30 minutes.

[0027] The above-described exemplary method allows diffusion bonding(specifically, solid state diffusion of aluminum between target 50 andbacking plate 60), as well as development of grains within target 50.Such grains form due to cold work introduced in target 50 during thecompression of FIG. 3. The grain development typically involves threedistinct steps. First, recovery in which stresses are relieved from inthe most severely deformed regions. Second, the cold-worked grainsrecrystallize forming small, new, stress-free grains in target 50, andfinally grain growth of the new grains occurs. Preferably, target 50 isnot exposed to a temperature above about 280° C. from the time it iswork-hardened in the step of FIG. 3, until it is exposed to the thermaltreatment. Accordingly, substantially an entirety of the graindevelopment of target 50 occurs during the thermal treatment of target50 and backing plate 60. The phrase “substantial entirety” is utilizedin referring to the recrystallization and grain growth occurring duringthe thermal treatment, rather than stating an “entirety” of therecrystallization and grain growth to indicate that there may be a smalland effectively inconsequential amount of recrystallization and graingrowth occurring at temperatures below 280° C. during processing andcleaning of target 50 prior to the thermal treatment.

[0028] A particular process for accomplishing the above-discussedthermal treatment method is to place the assembly of the target andbacking plate in a can (for instance, a can made of thin-walledaluminum), and to retain the assembly in the can during the heating andforging (i.e., pressing) associated with the diffusion bonding. The canpreferably comprises two parts, and a wide flange which allows forsubsequent welding to seal the target and backing plate assembly in thecan. Also, the can preferably has a small diameter tube which allows forvacuum checking of a weld seal on the can, as well as for providing avacuum or inert atmosphere inside the can. Once the target and backingplate assembly is provided in the can, the can is welded shut. An inertgas or vacuum can be utilized during the welding to alleviate oxidationof the target and backing plate assembly. Weld integrity can bedetermined by conducting a leak test using the small diameter tube. Afinal weld can be done on the small diameter tube to allow a vacuum orinert gas atmosphere to be maintained in the can. During the time thatthe target and backing plate assembly is subjected to diffusion bonding,a temperature of the assembly can be monitored indirectly by monitoringthe temperature of a so-called dummy part having the same dimensions asthe target and backing plate assembly, and heated in either the samefurnace as the assembly, or in an identical furnace.

[0029] After the thermal treatment of the target and backing plateassembly, such assembly is cooled. The cooling can be accomplished byexposing the assembly to either a liquid or a gas, with an exemplaryliquid being water, and an exemplary gas being air.

[0030] The methods discussed above can form a target and backing plateassembly 70 comprising a strong diffusion bond between target 50 andbacking plate 60, with a tensile strength of such bond being at least5,000 psi, and typically being between about 8,000 psi and 10,000 psi.The yield strength of fully recrystallized high purity aluminum is 3,000psi, which is about equivalent to 20 megapascals (MPa) and the ultimatetensile strength is 12 ksi (81 MPa). The yield strength of 6061 T4 is 21ksi (145 MPa), and the ultimate tensile strength of 6061 T4 isapproximately 35 ksi (241 MPa).

[0031] The diffusion bond can have a strength close to that of theultimate tensile strength of high purity aluminum, with the bondfrequently having a strength of from about 68.5% to about 83% of thetensile strength of the high purity aluminum utilized in the target(typically from about 8230 psi to about 9948 psi at room temperature).In contrast, solder bonds typically have strength ranges from about 1470psi to about 6740 psi. Bonds formed by methods of the present inventioncan therefore be significantly stronger than solder bonds, andaccordingly, better suited for the long-throw target applications ofmodern sputtering applications that were discussed in the “Background”section of this disclosure.

[0032] The backing plate preferably remains strong after theabove-discussed diffusion bonding. In a particular embodiment, a 6061backing plate was found to retain a minimum strength equal to 6061-T4when subjected to diffusion bonding at a temperature of about 300° C.

[0033] In addition to the strong bond formed between target 50 andbacking plate 60 of assembly 70, a grain size of target 50 is preferablybelow 100 microns, more preferably from about 30 to less than 100microns, and more preferably below about 50 microns after the diffusionbonding. Specifically, a predominate (i.e., more than 50%) of the grainsin target 50 will preferably have a maximum dimension of less than 100microns, more preferably from about 30 microns to less than 100 microns,and more preferably less than about 50 microns. In particularembodiments, an entirety of the grains in target 50 have a maximumdimension of less than 100 microns, more preferably from about 30microns to less than 100 microns, and more preferably less than about 50microns.

[0034] The above-discussed small grain size can be accomplished bystarting with a target which been cold-worked, but which does not havegrains formed. Accordingly, a recrystallization process will occur inthe target material prior to growth of grains. For aluminum, suchrecrystallization process typically takes from about 20 to 30 minutes ata temperature of between 288° C. and about 316° C. Thus, a target willspend a significant amount of time that it is at a diffusion bondingtemperature in a stage where grains are recrystallizing, rather thangrowing. Such can prevent the grains from over-growing during thediffusion bonding to sizes that are, for example, in excess of 100microns.

[0035] Experiments have been performed to determine if increases inprocessing temperatures or times improve bonding of targets to backingplates. It is found that if a target is treated with higher temperaturesor longer times, dramatic increases in grain size can occur, but onlyminor increases in bond strength are found.

[0036] It is to be understood that although several of the particularaspects described above pertain to first and second masses comprisingaluminum, the invention can be utilized with masses other than thosecomprising aluminum. It is preferred that the masses comprise acomponent in common to enable diffusion bonding between the masses.Specifically, if the masses comprise a component in common, then thecomponent can diffuse as a solid from one of the masses to another ofthe masses. The first and second masses can also comprise no commoncomponents, but diffusion between materials having the same component(known as self-diffusion) is typically faster than diffusion betweenmaterials comprising only dissimilar components. In particularembodiments, the masses will comprise an element in common, such as, forexample, elemental aluminum.

[0037] In compliance with the statute, the invention has been describedin language more or less specific as to structural and methodicalfeatures. It is to be understood, however, that the invention is notlimited to the specific features shown and described, since the meansherein disclosed comprise preferred forms of putting the invention intoeffect. The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A method of bonding a first mass to a second mass, comprising:providing a first mass of first material and a second mass of secondmaterial; joining the first mass and the second mass in physical contactwith one another; and simultaneously diffusion bonding the first mass tothe second mass and developing grains of the second material in thesecond mass, the diffusion bonding comprising solid state diffusionbetween the first mass and the second mass, a predominate portion of thedeveloped grains having a maximum dimension of less than 100 microns. 2.The method of claim 1 wherein all of the developed grains have themaximum dimension of the less than 100 microns.
 3. The method of claim 1wherein the maximum dimension of the predominate portion of thedeveloped grains is less than or equal to about 50 microns.
 4. Themethod of claim 3 wherein all of the developed grains have the maximumdimension of the less than or equal to about 50 microns.
 5. The methodof claim 1 wherein the maximum dimension of the predominate portion ofthe developed grains is from about 30 microns to less than 100 microns.6. The method of claim 5 wherein all of the developed grains have themaximum dimension of from about 30 microns to less than 100 microns. 7.The method of claim 1 wherein the first material comprises a samepredominate component as the second material.
 8. The method of claim 1wherein the first material comprises a same predominate element as thesecond material.
 9. The method of claim 1 wherein the bonded first andsecond masses correspond to a backing plate and a physical vapordeposition target, respectively.
 10. A method of bonding a physicalvapor deposition target material to a backing plate material,comprising: joining the target material and backing plate material inphysical contact with one another; and thermally treating the joinedtarget and backing plate materials to simultaneously diffusion bond thetarget material to the backing plate material and develop grains in thetarget material, the diffusion bonding comprising solid state diffusionbetween the backing plate and target materials, a predominate portion ofthe developed grains having a maximum dimension of less than 100microns.
 11. The method of claim 10 wherein all of the developed grainshave the maximum dimension of the less than 100 microns.
 12. The methodof claim 10 wherein the maximum dimension of the predominate portion ofthe developed grains is less than or equal to about 50 microns.
 13. Themethod of claim 12 wherein all of the developed grains have the maximumdimension of the less than or equal to about 50 microns.
 14. The methodof claim 10 wherein the maximum dimension of the predominate portion ofthe developed grains is from about 30 microns to less than 100 microns.15. The method of claim 14 wherein all of the developed grains have themaximum dimension of from about 30 microns to less than 100 microns. 16.The method of claim 10 wherein the backing plate material comprises asame predominate component as the target material.
 17. The method ofclaim 10 wherein the backing plate material comprises a same predominateelement as the target material.
 18. The method of claim 10 wherein thebacking plate material and target material both predominately comprisealuminum.
 19. The method of claim 10 wherein the grain developmentcomprises recrystallization of grains within the target material. 20.The method of claim 10 wherein the grain development comprises growth ofgrains within the target material.
 21. The method of claim 10 furthercomprising, before the joining, work-hardening the target material. 22.The method of claim 10 further comprising, before the joining,work-hardening the target material by compressing the target materialfrom an initial thickness to a final thickness, the final thicknessbeing less than or equal to about 40% of the initial thickness.
 23. Themethod of claim 10 further comprising, before the joining,work-hardening the target material by compressing the target materialfrom an initial thickness to a final thickness, the final thicknessbeing from about 40% to about 2% of the initial thickness.
 24. Themethod of claim 10 further comprising, before the joining,work-hardening the target material, and wherein the grain developmentcomprises recrystallization of grains from the work-hardened material.25. The method of claim 10 further comprising, before the joining,work-hardening the target material, and wherein the grain developmentcomprises: recrystallization of grains from the work-hardened material;and growth of the recrystallized grains.
 26. A method of forming aphysical vapor deposition target bonded to a backing plate, comprising:joining a physical vapor deposition target material and backing platematerial in physical contact with one another, the physical vapordeposition target and backing plate materials both comprising aluminum;and thermally treating the joined physical vapor deposition target andbacking plate materials under an atmosphere which is inert relative toreaction with the physical vapor deposition target and backing platematerials, the thermally treating simultaneously diffusion bonding thephysical vapor deposition target material to the backing plate materialand developing grains in the physical vapor deposition target material,the diffusion bonding comprising solid state diffusion between thebacking plate material and the physical vapor deposition target materialto adhere the physical vapor deposition target material to the backingplate material with a bond strength of at least about 5000 pounds/inch²,and a predominate portion of the grains developed in the target materialbeing less than 100 microns in maximum dimension after the thermallytreating of the target and backing plate materials.
 27. The method ofclaim 26 wherein the backing plate material and physical vapordeposition target material both predominately comprise aluminum.
 28. Themethod of claim 26 wherein the grain development comprisesrecrystallization of grains within the physical vapor deposition targetmaterial.
 29. The method of claim 26 wherein the thermally treatingcomprises maintaining the joined physical vapor deposition targetmaterial and backing plate material at a temperature of from about 280°C. to about 400° for a time of from about 20 minutes to about 60 minutesand pressing the joined physical vapor deposition target and backingplate materials to a pressure of at least 12,500 pounds/in² during atleast part of the time that the temperature is maintained.
 30. Themethod of claim 29 further comprising cooling the joined physical vapordeposition target and backing plate materials with a liquid after thetemperature treatment.
 31. The method of claim 29 further comprisingcooling the joined physical vapor deposition target and backing platematerials with a gas after the temperature treatment.
 32. The method ofclaim 26 wherein the grain development comprises growth of grains withinthe physical vapor deposition target material.
 33. The method of claim26 further comprising, before the joining, work-hardening the physicalvapor deposition target material.
 34. The method of claim 26 furthercomprising, before the joining, work-hardening the physical vapordeposition target material by compressing the physical vapor depositiontarget material from an initial thickness to a final thickness, thefinal thickness being less than or equal to about 40% of the initialthickness.
 35. The method of claim 26 further comprising, before thejoining, work-hardening the physical vapor deposition target material bycompressing the physical vapor deposition target material from aninitial thickness to a final thickness, the final thickness being fromabout 40% to about 2% of the initial thickness.
 36. The method of claim26 further comprising, before the joining, work-hardening the physicalvapor deposition target material, and wherein the grain developmentcomprises recrystallization of grains from the work-hardened material.37. The method of claim 26 further comprising, before the joining,work-hardening the physical vapor deposition target material, andwherein the grain development comprises: recrystallization of grainsfrom the work-hardened material; and growth of the recrystallizedgrains.